HDF-South Project at ESO

Introduction

ESO plans to obtain deep imaging observations in the HDF-South area. As part of the EIS project, the SUSI2 optical imager (300-1000 nm) and the SOFI infrared imager (1000-2500 nm) at the NTT will be used for broad band observations of a large area (three 5'x5' fields) spanning the regions covered by the STIS, WFPC2, and NICMOS fields of view. The ESO OPC has allocated time to this project during the months of August and September 1998.

In addition, during the Science Verification Phase of UT1 in August 1998, the VLT Test Camera (300-1000 nm) at the Cassegrain focus will be used to collect broad-, intermediate-, and narrow-band images in the same area. Both imaging and spectroscopic observations of the HDF-S area are also being considered for the science verification phase of the VLT FORS instrument.

All these observations are designed to complement the HST data and to expand their scientific output. Through these pages, we intend to provide information on the scope of the ESO HDF-S observations and to describe their characteristics.

Summary of the Scientific Objectives

NTT wide field survey

These observations are aimed at providing 8 broad band colors over three areas of 5'x 5' each to select candidates for spectroscopic follow-up with FORS and ISAAC. The imaging over the WFPC2 field is intended to complement the very deep HST observations with IR magnitudes to allow for accurate photometric redshift measurements.

NIC3 field with the VLT-TC

These observations should complement the NIC3 and STIS data in the optical. The goal is to go as deep as possible with the Test Camera (FOV 90"x90") to reach limits which are interesting in comparison with the HST deep observations. A set of 910nm-band frames will complement imaging in the other bands and make photometric redshift determinations more accurate. The morphological information provided by the observations conducted with STIS on this field can be used to deconvolve the TC data.

STIS field with the VLT-TC

A deep image through a narrow-band filter will be used to detect extended Ly-alpha emission associated with the QSO as well as emission line galaxies at the same redshift.

NTT Observations

The two instruments will cover three fields (5'x5' each), including the STIS, WFPC2, and NIC3 fields. The coordinates of the three pointings are:

Field

Coordinates J2000

STIS

RA: 22 33 32.5

DEC: -60 33 30

WFPC2

RA: 22 33 00.0

DEC: -60 33 30

NICMOS

RA: 22 33 00.0

DEC: -60 38 30

The exposures times in seconds planned on each of the three fields are indicated in the table here below (seeing of 0.8 arcsec is assumed):

Band

Lim AB mag
(5 sigma)

Exp. Time
(individual)

Exp. Time
(total)

Filter

U

26.8

1200

18000

SUSI2 U

B

26

900

6500

SUSI2 B

V

26

600

5400

SUSI2 V

Rw

26.3

600

5400

SUSI2 #825

I

26.5

600

12600

SUSI2 I

J

24.3

-

10800 (*)

SOFI J

H

23.9

-

10800 (*)

SOFI H

Ks

23.4

-

10800 (*)

SOFI Ks

(*) The pointing including the WFPC2 field should have exposure times twice as long in Ks, thus reaching 1 mag fainter.

N.B. Should the seeing be worse than 1.3 arcsec, EIS U band observations will be performed instead.

The total time for this project (including overheads but assuming perfect weather conditions) corresponds to approximately 40 hour of SOFI and 47 hour of SUSI2 observations. The priority for SUSI2 observations, in order of decreasing importance, is as follows: QSO field, WFPC2 field, NICMOS field. For SOFI the order is: WFPC2 field, QSO field, NICMOS field. Integrations on higher priority fields should be at least 80 % complete in all colors before moving to another field. Observations through the Rw (R wide) band have the highest priority, compatibly with moon constraints.

VLT-TC Observations

These observations have been allocated five nights during the VLT Science Verification that will take place between August 17 and August 31. It is planned to observe two pointings centered on the STIS and NIC3 field, respectively. Observations in UBVRI to limiting magnitudes near 28 are planned for the NIC3 field. In addition, a long exposure with an intermediate band filter center on the OH-free window at 910nm will be obtained at the same position. The STIS field is planned to be observed through a narrow band filter centered at the Ly-alpha of the QSO (~392 nm @ z~2.22) and through the B band. The table below gives the estimated time in seconds to reach the quoted AB magnitudes (assuming seeing of 0.7 arcsec).

Band

Lim AB mag
(5 sigma)

Exp. Time
(individual)

Exp. Time
(total)

Filter

U

27.5

900

32400

VLT-TC U

B

28.5

600

10800

VLT-TC B

V

28

600

10800

VLT-TC V

Rw

28

300

10800

SUSI2 #825

I

28

300

14400

VLT-TC I

910/30

26.9

900

28800

SUSI2 IB

392/7

26 ?

900

14400

special narrow band
at Ly-alpha of QSO

The observations described above require about 40 hour of telescope time, including overheads. More information on these observations is available on the Science Verification Observation Blocks page.